Prior art pointing devices such as a joystick are known. What others have failed to appreciate is the ergonomic implications of mechanical and electrical null regions which must be traversed at the outset of a pointing operation. Using prior art devices, even those that are force-sensitive, a user gets no response to lateral displacement initially, until an electrode makes initial contact, for example, with an elastomeric resistive layer. The initial contact causes a step response, as resistance drops from infinity to a measurable value--a jump the user may not have anticipated or desired. Then, as force is increased, resistance falls rapidly, over some range, and finally falls more slowly with the application of additional force. All of this is disconcerting to a user for most applications. What is needed is to provide for pointing which is smoothly and consistently responsive to user input from the outset of the pointing operation by controlling such null regions.
Another disadvantage associated with prior art pointing devices is that they are not sensitive to vertical or z-axis force. Forces applied laterally, i.e., in the x-y axis plane, move a cursor in the corresponding direction on a computer or other information display screen. It would be desirable for a vertical force, e.g., down the shaft of a joystick-type controller, to produce a proportional signal. Such a signal could be used for example to control line width while drawing as a function of z-axis force on the pointing device. Z-axis force could also be used to control speed or acceleration of a cursor or apparatus being manipulated.
One prior art cursor control device is shown in U.S. Pat. No. 4,313,113 to David Thornburg. It employs four orthogonal variable-resistance pressure transducers, each transducer comprising a coordinate electrode spaced from a cooperating electrode, at least one of the electrodes being an elastomeric sheet material formed of a carbon loaded polyolefin. The path resistance through the transducer goes down as applied pressure goes up. However, the electrodes are spaced from the elastomeric layer, at rest, so that there is a mechanical and electrical null region before the system responds to a force input, followed by a step response when the electrode layers make initial contact. These characteristics are disconcerting to a user and therefore undesirable for accurate control.
U.S. Pat. No. 4,439,648 (Reiner et al.) is directed to a basic stand-alone joystick. The handle rests on a rigid pivot so that vertical force is ignored. The handle is coupled to an actuator portion spaced from all four switches, so there is a neutral or null region of displacement before any switch is closed. The switches are conventional, yielding only a binary signal, without regard to force.
U.S. Pat. No. 4,408,103 (Smith, III) discloses a miniaturized joystick adapted for mounting in a wristwatch. The joystick handle rests in a hollowed-out bearing surface so that none of the switches is actuated by a downward force on the handle. The switch actuating means is maintained spaced from all the switches by a resilient rubber sheet layer, so once again there is a neutral or null region of displacement before any of the switches is closed. The switches are miniaturized by forming them as interleaved electrodes on a PCB. When the handle is pivoted, an actuator pushes a conductive region of the resilient layer into contact with a corresponding switch. The switches each yield a binary output, so lateral force beyond an initial detect is ignored.
U.S. Pat. No. 4,246,452 (Chandler) shows another joystick type device, here having 16 possible output signals. The mechanism again employs a handle having a depending member that rests in a hollowed out bearing surface. Once again, the switches each provide a binary signal, independent of lateral force beyond a threshold force; vertical force is ignored; and, the actuator is spaced from the switches to provide a null region.
U.S. Pat. No. 4,680,577 (Straayer et al.) discloses a multipurpose keyswitch that serves both as a regular typing key, preferably located in the "home row" (asdf-jkl;) of a keyboard, as well as a force-sensitive pointing device. The use of strain gauges as shown therein for force sensing, however, is not commercially practical. Additionally, the recent rise in popularity of portable lap-top, notebook and even "palm-top" computers makes low profile methods essential. Straayer et al. also suggests activating the cursor positioning capabilities of the multipurpose keyswitch by first closing an additional keyswitch on the keyboard. A separate keyswitch for that purpose, however, is cumbersome to use. By comparison, the conventional mouse is essentially always "ON" for receiving pointing input. Moreover, keyboard space is at a premium in today's small portable computers, so an additional dedicated key is to be avoided if possible.
The parent application identified above discloses a keyswitch-integrated pointing device, for example, a computer keyboard typing key having force sensors coupled to it so that the typing key can also function somewhat like a joystick for controlling a cursor. Such a "multipurpose keyswitch" presents mechanical design challenges in order to maintain a normal "feel" or tactile response of the keyswitch for typing operations. In other words, the joystick feature must be carefully implemented so as to not interfere with the typing performance of the selected keyswitch.
Another problem with an input system that employs a multipurpose keyswitch is detecting when the user is "pointing". In conventional systems, such as the ubiquitous personal computer of the 1980's, the pointing device (typically a "mouse" separate from the keyboard) provided pointing information (cursor displacement data) through a dedicated mouse input port separate from the keyboard input port. That architecture segregates pointing data from typing data. Since the two input channels operate in parallel, both typing and pointing functions are always enabled. A multipurpose keyswitch can only provide one function at a time. Which function the user intends (typing or pointing) must somehow be determined. A separate switch to enable the pointing function is undesirable for reasons stated above. The need remains, therefore, for improvements in joystick methods and apparatus to provide accurate pointing operations and other benefits discussed below, all at low cost.